Among the changes Montgomery has made are shifts in the momentum models. Momentum screens favor stocks that have been rising. The approach can work because under normal circumstances, stocks that are moving up tend to keep climbing over the short term. But when markets collapse suddenly, stocks with strong momentum can sink hard. "Momentum can be a lousy indicator at market inflection points," says Montgomery.It is too soon to know whether Montgomery's tweaks will prove successful over the long term. But if markets remain stable, Bridgeway and other active managers could have a better chance of success. This article is commentary by an independent contributor, separate from TheStreet's regular news coverage.